The present invention relates to ball seals. More particularly the invention relates to seals of the type having a ball-shaped metal housing in which the ends of a flexible metal strap may be permanently locked such that the device must be broken to be opened and thus reveal tampering.
The ball seal has found wide spread use as a reasonably reliable means for sealing the doors of railroad freight cars, trucks, and similar containers. Examples of prior art ball seals may be found in the following U.S. Pats. No. 4,424,995; No. 4,690,444; and No. 4,093,287. These patents show various modifications of the basic sealing structure. These modifications are primarily directed at improvements in two areas, viz. reducing the vulnerability of such seals to tampering and reducing manufacturing costs.
Although most prior art varieties of ball seals have been judged relatively tamper resistant and have been used extensively because of their low cost, they have not proved entirely satisfactory under all circumstances. One critical problem confronting the developers of such seals has been the problem of preventing tampering through the reconstruction or repair of previously used, discarded seal parts by unauthorized people.
More specifically, the recommended method of opening ball seals is to cut the metal strap or shackle, remove the seal from the container being sealed, and discard the broken seal. Another method of removing such seals is by pulling the metal strap or shackle from the seal housing to force the straps and other parts out of the housing. When this latter method is used, the strap and the locking structures contained in the housing are forced through the housing opening, thereby ripping the housing and causing a large gap in the housing through which the strap and locking structure pass. The first method of removal results in a cut strap and an undamaged housing. Conversely, the second method results in a damaged housing and an undamaged strap. In both cases, the locking structure remains substantially undamaged or only slightly bent and often easily repairable. As such, those concerned with the development of such structures have recognized the vulnerability of such seals to undetected tampering since an enterprising intruder could easily acquire discarded parts, reconstruct a workable seal, and then use this seal to reseal a container entered illegally.